1. Technical Field
The present invention relates to a weld structure that joins a first member and a second member by welding.
2. Related Art
A vehicle is equipped with a differential device, such as a front differential and a rear differential, which distributes a driving force output from an engine to corresponding left and right drive wheels when turning or the like. Also, as another form of the differential device, there is a center differential that distributes a driving force output from an engine to front and rear drive wheels. The differential device includes a differential ring gear to which a driving force is transmitted, and a differential case joined with the differential ring gear to rotate integrally with the differential ring gear. As a joining method of the differential ring gear and the differential case, there is a joining method by welding, in addition to a combining method by bolts or the like. For example, the differential ring gear and the differential case are joined, by performing beam welding to a position at which the differential ring gear made of carbon steel and the differential case made of cast iron are in contact with each other.
At the welding position of the differential ring gear and the differential case, a beam entering side is formed in a groove shape, and a space is formed at the back of the welding position at a beam distal end side. At the time of beam welding, a high energy beam is radiated while a filler wire is supplied to a groove, and penetration welding that causes melt metal to reach the space is performed. In this case, heat input at the time of welding increases the pressure in the space at the back of the welding position, and gas blows out from a part of the melt metal, and a defective hole opens in the weld portion in some cases. Hence, in order to reduce rise of the internal pressure of the space, there is a proposed differential device that is provided with a hole or a gutter that causes the space to communicate with outside (refer to Japanese Unexamined Patent Application Publication No. S61-95796, WO 2013/018223, and Japanese Unexamined Utility Model (Registration) Application Publication No. H3-14066).
Here, when the differential ring gear and the differential case are joined together, an outer circumferential portion of the differential case is press-fitted into an inner circumferential portion of the differential ring gear, and welding is performed to an abutting surface between the differential ring gear and the differential case, in order to maintain the precision of the differential ring gear. In this case, in order to prevent galling in the press fit surface, a gutter for gas releasing is not provided on the press fit surface, but it is necessary to provide a communication hole that communicate between the space and the outside.
However, when the communication hole that communicates between the space and the outside open to atmospheric air is provided, it is concerned that foreign objects, such as press fit powder generated at the time of press fit of the differential case and the differential ring gear and sputtered material generated at the time of welding, are ejected to the outside via the communication hole, after the differential device is installed in the transmission device. Such foreign objects get mixed into the inner portion of the transmission device as contaminants. In order to prevent ejection of such foreign objects, the communication hole needs to be blocked by the time when the differential device is installed in the transmission device at least, and therefore it is concerned that an additional process such as inserting a plug into the communication hole is necessary and that the production cost rises.